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On Mars, More Water From Pricey Plumbing

25.08.2004

NASA decides to send astronauts to Mars and farther out, one of the biggest technological hurdles it will face will be making sure they don’t get thirsty.

A $49,000 toilet at Purdue University may provide part of the answer. When NASA engineers first considered manned missions to Mars to follow the moon landings, they imagined that the astronauts would simply pack lots of water and food.

"We could go to Mars with Apollo technologies," said Dr. Daniel J. Barta, deputy manager of the advanced life support office at NASA’s Johnson Space Center in Houston. But the high cost of sending something from Earth to Mars led to estimates of $1 trillion for a Mars mission.

Since then, engineers have looked to slash weight and costs through draconian recycling of air, food and particularly water, with the spacecraft perhaps carrying as little as 1,000 gallons of water per astronaut for a trip that would take six months one way. (By contrast, the typical American uses about 100 gallons of water a day.) "They’ve got to make that last," said Dr. Jeffrey J. Volenec, a professor of agronomy at Purdue, "so recycling is going to be important." That includes making sure that what goes down the toilet comes back up as water and food.

As part of a five-year, $10 million, NASA-financed program for developing technologies to survive lengthy space travel, researchers at Purdue have built a Rube Goldberg system using plants and bacteria to transform feces and urine into plant fertilizer and clean water.

The contraption begins with a converted portable restroom on the third floor of Purdue’s civil engineering building, in a laboratory of Dr. James E. Alleman. Inside the stall, on loan from NASA, is the toilet, similar to ones on airliners that use a vacuum instead of water to empty the bowl. For the advancement of science, people donate their bodily wastes. "We have a bunch of volunteers," Dr. Alleman said. "They’re anonymous."

The volunteers deposit their urine down one pipe, where it is collected and partially frozen. The frozen portion is almost pure water ice; the impurities are left in the remaining unfrozen liquid.

The system currently recovers 30 percent of the water in urine, and Dr. Alleman believes that the yield can be raised to nearly 90 percent. "We recover almost pure water out of the urine," Dr. Alleman said. "It’s drinkable."

Meanwhile, the feces go down the toilet into a storage tank on the second floor. The researchers add plant and food waste that the astronauts would likely also need to dispose of. From there, the waste flows to a cylindrical container familiar to college students. "It is a small beer keg," Dr. Alleman said. "We have a limited budget." This particular keg, heated to 140 degrees, kills harmful microbes. "It’s much like pasteurizing milk," he said. Other bacteria in the keg thrive in heat and eat the waste.

After 10 days of the bacteria munching on the mix, the result is 97 percent water and 3 percent residual solids. "You can’t shower with that or eat it," Dr. Volenec said. While not putrid, he said, "It smells odd." He added, "Somewhere between a gym locker and sewage." One way to purify the water would be to boil it and then condense the steam, but that would consume large amounts of energy. The Purdue scientists look to plants to do the job instead.

Dr. Volenec takes the liquid from Dr. Alleman’s keg and spreads it onto plants. The residual solids fertilize the plants, and the plants pull water from the soil into their roots up through their stems into their leaves, where the moisture evaporates in the air. Cold pipes above condense the vapor, producing clean recycled water.

So far, the project has been a "moderate success," Dr. Volenec said. Tomatoes and peppers did not grow well in the sewage mixture, but rice and some marsh grasses have.

The processed sewage mixture could also be used for raising fish or for growing mushrooms. Dr. Barta, of NASA, said that the first astronauts would probably subsist mostly on packaged food, but that "having some fresh components would have a lot of appeal."

Using plants to cleanse the water and air on a spacecraft would add a new level of complexity, however. If the plants died, the astronauts would die, too. "We have to get the systems to function reliably for a long period of time," Dr. Barta said. "We can’t come back to Earth and fix them." Kenneth Chang

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